1. Field of the Invention
The present invention relates to a reversal development processing method for black and white silver halide photographic light-sensitive materials and, more particularly, to a means for accelerating bleaching in reversal development processing of light-sensitive materials.
2. Description of the Prior Art
As is disclosed in "Kagakushashinbinran chu", pp. 69 to 71 (published by Maruzen, Japan), it is well known that positive images can be obtained by reversal photographic processing which comprises developing an imagewise exposed light-sensitive material to form silver images, removing the silver images by bleaching, exposing the undeveloped silver halide and developing the silver halide. Since a reversal processing method provides positive images directly by development, it is useful in the reproduction fields such as for reproducing movies, documents, drawings, etc.
It is essential in reversal processing of light-sensitive materials that silver images are completely removed by bleaching after the silver images are formed by developing the latent images formed in the light-sensitive materials by imagewise exposure. In photographic processing fields, a so-called color light-sensitive material is also processed by a method including a bleaching step. However, silver images are not necessarily removed in the bleaching step of color light-sensitive materials. For example, silver images can be rehalogenated to silver halide which is then fixed and removed. On the contrary, if silver images of a black and white light-sensitive material are not completely removed in the bleaching step, the exposed areas are no different than the unexposed areas after forming the reversal images by second development of the silver halide undeveloped by the first development, and, as a result, unacceptable reversal images having much fog and less contrast are formed.
As a bleaching solution for black and white light-sensitive materials, a composition is available containing an oxidizing agent for silver images such as permanganate, persulfate, bichromate, ferricyanide, cerium salt, ferric salt, cupric salt, a metal complex salt of an aminopolycarboxylic acid, etc., or mixtures thereof. Of these compounds, a heavy metal compound such as permanganate or bichromate, and a compound having a cyanide ion such as ferricyanide are not preferably employed because they can be harmful to animals and plants when they occur in waste water, etc. A metal complex salt of an aminopolycarboxylic acid, on the other hand, is not a preferred bleaching agent for black and white reversal processing because the speed with which it bleaches developed silver is slower than other bleaching agents and because the monovalent silver formed by bleaching is not converted into a water-soluble compound, and oxidized silver is not removed from the light-sensitive materials.
A ferric salt, a cerium salt and a persulfate are preferred bleaching agents for black and white light-sensitive materials because they do not present pollution problems and because they convert monovalent silver to a water-soluble silver compound. However, their bleaching speed for black and white light-sensitive materials is not satisfactorily fast. Particularly, where they are employed for rapid processings, the bleaching speed of the compounds is insufficient because the bleaching time plays a large part in the total processing time. For example, the developing step, stopping step and fixing step of reversal processing in making microfilm are completed in several seconds to several tens of seconds, but the bleaching step using a bleaching agent other than a bichromate and a ferricyanide takes at least 30 seconds and in many cases more than several minutes. In other words, an oxidizing agent capable of converting developed silver into a water-soluble silver compound without pollution problems such as a ferric salt, a cerium salt or persulfate may not be suitable for a rapid reversal processing of black and white light-sensitive materials due to its low bleaching speed.